Conventionally, in a motor such as a motor for an EGR (Exhaust Gas Recirculation) valve, in order to detect the rotational position of a motor rotor with high precision by a position detection hole sensor, the motor rotor and the magnet assembly for the position detection hole sensor are fastened without looseness. Specifically, the top end portion of the motor rotor is first press-fit into a fastener hole formed in the magnet assembly. As a result, it is possible to ensure the whirl-stop strength between the motor rotor and the magnet assembly. Then, a tip resin part protruding from the motor rotor through the fastener hole of the magnet assembly is subjected to ultrasonic staking, and the tip resin part is melted to perform cover latching at the top of the magnet assembly. This can ensure the slip-off stop strength in the axial direction of the magnet assembly to the motor rotor (for example, see Patent Document 1).